The present integrated circuit devices comprise a silicon substrate, doped regions in the substrate to which source or drain connections are made, separated by a gate control region. Metal connections to the source, gate, and drain electrodes is made by multilayer interconnects, which are supported over the substrate by an interlayer dielectric.
The integrated circuit device speed is a function of the RC (resistance and capacitance) time constant of the multilayer metal interconnect. For a higher speed performance, the RC time constant must be reduced. The dielectric material used in the interlayer structure is typically silicon dioxide, which has a dielectric constant about 4, and it is the source of C (capacitance). The interconnect material is typically aluminum or, more commonly, an aluminum alloy including a small amount (about 1%) of copper, silicon, or titanium. The interconnect material typically comprises a multilayered structure of titanium/titanium nitride/aluminum (alloy)/titanium nitride, such as, for example, Ti/TiN/Al-1% Cu/TiN. The interconnect layer is the source of R (resistance).
In order to achieve an increase in device speed, the RC time constant must be reduced. A reduction in the RC time constant may be achieved by decreasing the capacitance C or the resistance R or both.